Screen combination

ABSTRACT

THE HEAD LINES OF THE SCREENS ARE USED IN PRINTING A PICTURE ARE PREFERABLY SLANT AND AT DIFFERENT ANGLES IN RELATION TO THE HEAD LINES OF THAT PICTURE. EVERY SCREEN DOT OF SUCH A SCREEN IS OBTAINED AT THE DEVICE DESCRIBED BY EXPOSURE OF A PHOTO-SENSITIVE LAYER, WHICH IS PROVIDED ON TO AN ETCHABLE SUBSTRATE, WITH THE AID OF AN ELECTRON BEAM. IN THE PROCESS A HEAD LINE OF THE PICTURE MOVES ACCORDING TO ITS OWN LENGTHWISE DIRECTION IN A PLANE PERPENDICULAR TO THE OPTICAL AXIS OF THE ELECTRON GUN. BY RENDERING THE ELECTRON BEAM FOR MANUFACTURING SPECIFIC DOTS OF THE SCREEN A DEVLINATION PERPENDICULAR TO THE SAID HEAD LINE AND/OR IN THE DIRECTION OF THE SAID HEAT LINE OF THE PICTURE A SCREEN IS CREATED WITH ITS TWO HEAD LINES SLANT IN RELATION O THE HEAD LINES OF THE PICTURE.

May 23, 1972 FQNTIJN 3,664,843

SCREEN COMBINATION Filed June 9, 1970 FIG.1

INVENTOR.

MWJMI ZV;

United States Patent US. Cl. 96-116 7 Claims ABSTRACT OF THE DISCLOSUREThe head lines of the screens used in printing a picture are preferablyslant and at different angles in relation to the head lines of thatpicture.

Every screen dot of such a screen is obtained at the device described byexposure of a photo-sensitive layer, which is provided on to an etchablesubstrate, with the aid of an electron beam.

In the process a head line of the picture moves according to its ownlengthwise direction in a plane perpendicular to the optical axis of theelectron gun.

By rendering the electron beam for manufacturing specific dots of thescreen a declination perpendicular to the said head line and/or in thedirection of the said head line of the picture a screen is created withits two head lines slant in relation to the head lines of the picture.

The invention relates to a screen combination comprising a basic screenwhose screen dots are placed on the angular points of squares and atleast one screen rotated in relation to the basic screen, whose screendots are also placed on angular points of squares.

Such a screen combination is known in the art.

This known combination comprises a screen that is rotated 15 in relationto the basic screen, a screen that is rotated 45 in relation to thebasic screen and a screen that is rotated 75 in relation to the basicscreen.

In order to obtain a rotated screen, the original of which a colourreproduction has to be made, is scanned, with regard to the intensity ofa colour, at an angle that is as great as the angle the rotated screenmust have in relation to the basic screen.

With the intensity-modulated signal a machine for engraving the rotatedscreen is fed. So in order to attain a screen combination the originalmust be scanned as many times and the engraving machine must be fed asmany times as there are screens applied in the combination.

So manufacturing a combination of such screens requires much time andtherefore is expensive.

The object of the invention is such a screen combination and with screenrotations chosenin such a way that the basic screen and the rotatedscreens can be engraved on a machine simultaneously with modulatedsignals originating from an original not rotated in relation to thebasic screen and attached to the same machine.

The invention is therefore characterized in that the screens show achange in lineature in relation to the unit of length=l according toformula W I-p in which parameter x is a scale factor, parameters n and pare whole numbers and parameter n at the same time depends on the anglethe head lines of the screens make with the edges of the pictures.

In order to attain simple electronics for and a simple qonstruction ofthe engraving machine for parameter ice n=1 the angular rotation ispreferably chosen equal to 45 degrees, for n=2 equal to 26 degrees and34 minutes, for n=3 equal to 18 degrees and 26 minutes and for n=4 equalto 14 degrees and 2 minutes.

The invention is preferably applied to a machine with rotatingcylinders.

Then on the jacket of one of the cylinders the original that has to bescanned is mounted. The other cylinders are provided on their jacketswith a layer to be exposed, which is exposed with a pulsating electronbeam.

Scanning the picture is ettected according to a helix with a pitch thathas been chosen identically to scale factor x multiplied with unit 1.

The screen dots to be engraved of rotated screens are not all of themlying on helices; by having small deviations of the electron beam makesmall deviations, all screen dots can be engraved after all.

So the rotated screens are engraved according to diagonal directions andangular dots that do not line on the diagonals are filled up by lateraldisplacements of the electron beam between the helices.

The invention will now further be elucidated with reference to a drawingwith 5 figures.

In the drawing:

FIG. 1 represents the screen known in the art mostly suitable for use asbasic screen.

FIG. 2 a screen according to a diagonal 1 over 1, also suitable as basicscreen.

FIG. 2a a screen as shown in FIG. 2, however, with x= /2.

FIG. 3 a screen according to a diagonal 1 over 2 to the left or to theright.

FIG. 4 a screen according to a diagonal 1 over 3 to the left or to theright.

FIG. '5 a screen according to a diagonal 1 over 4 to the left or to theright.

In FIG. 1 a so-called straight screen is drawn with the head linesparallel to the edges of the picture.

The screen dots are placed on the angular points of squares, with a sidelength equal to the unit=1.

Such a screen can easily be made on an engraving machine, the originalbeing mounted on a cylinder jacket and being scanned according to ahelix with a pitch equal to the unit=1 multiplied with a factor x, ifnecessary, and the screen being obtained by point-by-point exposure of alayer on a second synchronously running cylinder.

Starting from the original on the machine now according to the inventionit has become possible to manufacture simultaneously other screens whosehead lines make ditferent angles with the head lines of the basic screenas shown in FIG. 1.

For this purpose it will be necessary that the exposure apparatuses arecontrollable, so that screen dots do not lie on'the helices according tothe basic screen but somewhat outside of it and that moreover aresomewhat shifted in relation to this screen can be engraved.

A device as described in U.S.A. patent application No. 827,510, forinstance, is designable for the above purpose, by mounting to theelectron beam exposing apparatus as described in this application acontrol by means of which the electron beam can be moved in the plane ofengraving.

As will appear further the displacements must be effected in code, forthey are connected with the angle the screen must obtain with the edgesof the picture. The code can originate from a code disc that rotatesalong with the cylinder on which the original that is to be scanned ismounted.

For each part-colour in a colourprint the screen must make a specificangle with the edges of the picture.

If the original is composed of five colours then also five screens mustbe manufactured at five different angles.

For that purpose also five exposure apparatuses with five individualcodings for localization of the dots are required.

Further moreover each exposure apparatus still is simultaneously andindividually controlled in intensity by means of intensity-modulatedcolour signals obtained by scanning the original.

Q1 order to obtain a simple engraving apparatus the cy nders forengraving and the cylinder with the original a preferably mounted on toone shaft so that the drive and the pitch for engraving and scanning areidentical. This is shown in FIGS. 1 to 5.

In the figures the pitches of the helical scanning and engraving areindicated by the letter S.

The screen dots are placed on the angular points of squares: for thatpurpose pitch S has been taken equal to the unit of length==l. Then fora straight" screen as has been shown in FIG. 1 it holds that thedistance between the screen dots the so-called lineature is also equalto =1.

For a screen such as has been shown in FIG. 2, with the head linesrunning at 45 with the edges of the picture, the lineature becomes /2.Such a 1 over 1 screen (see the dotted lines in this figure) has only afew screen dots.

Coding is simple, again and again only one screen dot needs to be leftout when engraving dots P P P which all of them are lying on one helix.

In the screen with head lines at 45 according to FIG.

2a the lineature becomes x/T.

The number of screen dots has considerably been increased. Dots P and Pare again lying on one helix. For engraving the intermediate dot P theelectron beam must be moved by /z to the left.

The code for this is simple to realize.

The lineature of the so-called I over 2 screen shown in FIG. 3 becomesHere dot P is also obtained by control by means of coding the electronbeam of the engraving machine.

The lineature of the so-called 1 over 3 screen shown in FIG. 4 becomesma t-1m Dots P and P are obtained by movement of the electron beam tothe left while dots P and P are lying on a helix as a result of pitch S.

The lineature of the 1 over 4 screen shown in FIG. 5 is vm m m 4 T T afirst plate having picture points located at the corners of saidsquares,

a second plate having picture points located at the corners of saidsquares and the pattern of dots is rotated relative to the pattern ofdots of said first plate,

the lineation of said pattern of squares on each of said plates isformed according to the formula wherein x represents a scale factor, nand p are whole numbers in which n is a function of the lineation ofsaid squares with respect to the edges of the picture.

2. The combination of printing plates as in claim 1 wherein for an angleof '45 degrees 11:1 and n=1.

3. The combination of printing plates as in claim 1 wherein for an angleof 20 degrees 34 minutes 11:1 and 12:2.

4. The combination of printing plates according to claim 1 wherein foran angle of 18 degrees 26 minutes 12:1 and n=3.

5. The combination of printing plates as in claim 1 wherein the angle isequal to 14 degrees 2 minutes for p='1 and "=4.

6. The combination of printing plates as in claim 1 wherein said firstplate has headlines running parallel to the edges of said picture inmagenta, said other plate represents cyanic, a third plate representinga screen wherein x=1 and n=2, and a fourth screen in yellow havingparameters 20:1 and n=3, and said second screen is rotated in onedirection with respect to said 'first screen, said third screen isrotated in the opposite direction with respect to said first screen, andsaid fourth screen is r0 tated in the same direction as said thirdscreen.

7. The combination of printing plates as in claim 1 wherein said firstscreen has headlines running parallel to the edges of said picture inmagenta, a second plate forming a screen in yellow with parameters x=1and n=2, a third plate forming a screen in black, and a fourth plateforming a screen in cyanic, said third and fourth screens havingparameters of x=1 and n= 3, said second screen is rotated in onedirection with respect to said first screen, said third screen isrotated in the same direction as said second screen and said fourthscreen is rotated in an opposite direction than said second screen withrespect to said first screen.

References Cited UNITED STATES PATENTS 2,757,087 7/ 1956 Wicklund 96-1163,085,878 4/1963 Archer 96--45 3,300,308 1/1967 Jemseby 96-45 2,864,7004/ 1958 Chevalier 9645 3,040,644 6/1962 Hearther 9645 3,210,186 10/ 1965Gorig 961l6 NORMAN G. TORCHIN, Primary Examiner E. C. KIMLIN, AssistantExaminer US. Cl. X.R. 96-4l, 44, 45

NITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION A Patent No.326641843 D t d May 3, 1972 I Inventor(s) Leendert FOntijn It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Claim 1: Line 13, should read: x n

Claim 3: Line 2, cancel 20" and insert --26-.

Claim 6: Line 2', after "wherein" insert -p l and--. Line 4, beforewherein insert --'in blaok--.

Claim 7: Line 2-, after "wherein" insert --p l" and--.

Signed and sealed this 9th day of July 1971.

(SEAL) Attest: v

McCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents PC4050 uscoMM-oc 60376-P69 ".5. GOVERNMENT PRINTING OFF'CE 2 9.90-366-334,

